Re: G3406 undervoltage at only 50% load

Does the engine speed drop when you apply load above 50%? If the engine speed remains stable, the issue sounds like a generator issue instead of an engine issue. If the engine speed is dropping with added load, this will cause the generator output voltage to decrease. If this is the condition, then you need to determine why the engine speed is dropping. Fuel supply pressure decreasing? Governor working correctly? Carburetor issue? Turbocharger or wastegate issue, if equipped with a turbocharger? As the load increases, the wastegate must stay closed to allow the turbocharger to build up boost to make the required horsepower to carry the load.

If the engine speed remains stable, the low voltage issue could be the generator regulator not maintaining output voltage as the load increases.